Warfarin potassium (1) is an anticoagulant and it is marketed in USA under the commercial name Athrombin-K™. Chemically, Warfarin potassium is monopotassium (RS)-2-oxo-3-(3-oxo-1-phenylbutyl)-chromen-4-olate. Warfarin is also known in the literature to exist as the Warfarin acid and Warfarin alkali metal salts such as sodium and lithium. Warfarin is marketed in the United States as Coumadin™ and Jantoven™. It is also marketed outside the United States as Marevan™, Lawarin™, and Waran™. Warfarin and Warfarin-alkali metal derivatives are also commonly used as rodenticides.

U.S. Pat. No. 2,765,321 discloses a process of making crystalline Warfarin sodium.
U.S. Pat. No. 2,777,859 discloses Warfarin-alkali metal derivatives and processes of preparing the same.
U.S. Pat. No. 3,077,481 (re issued as RE25866) discloses that when Warfarin sodium is in solution in A. R. isopropyl alcohol (C3H7OH, B. P. 82.4° C.), the Warfarin sodium reacts with the isopropyl alcohol to form a Warfarin sodium.isopropyl alcohol complex which crystallizes and is readily separated from the non-Warfarin impurities.
U.S. Pat. No. 3,192,232 relates to Warfarin known chemically as 3-(alpha-acetonylbenzyl)-4-hydroxy-coumarin and more specifically to improvements in the art and science of making and purifying Warfarin and alkali metal derivatives of Warfarin, e.g. Warfarin sodium, Warfarin potassium, and the like.
U.S. Pat. No. 3,246,013 discloses a process consisting essentially of neutralizing Warfarin in isopropyl alcohol with a compound represented by the formula RONa, where R is selected from the group consisting of hydrogen and alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tertiary butyl groups, i.e. lower alkyl groups containing 1-4 carbon atoms. The process is carried out by mixing or suspending Warfarin in excess isopropyl alcohol and slowly adding with rapid stirring the RONa compound to the resulting Warfarin-isopropyl alcohol slurry or suspension, warming the resulting reaction mixture, e.g. to 50-80° C., cooling the reaction mixture, e.g. allowing the warm reaction mixture to cool to room temperature, and recovering the crystalline Warfarin sodium.isopropyl alcohol complex after it crystallizes out of the cooled reaction mixture, e.g. by filtration.
U.S. Pat. No. 5,696,274 provides processes which are flexible, cost effective, and commercially viable methods of manufacturing for producing products from 2-hydroxyacetophenone (2-HAP). Of particular interest of the available products are 4-hydroxycoumarin, Warfarin-alkali salt, preferably Warfarin sodium and Warfarin-alkali salt-isopropyl alcohol (2-propanol) complex, more preferably Warfarin-sodium-isopropyl alcohol complex. As is known, these compounds are useful as vitamin K dependent anticoagulants in the treatment of humans and animals. In different doses, they are also useful as a rodenticide. The inventive process involves contacting 2-HAP, carbonate ester and effective base followed by treatment with an unsaturated ketone and phase transfer catalyst to ultimately yield product.
U.S. Pat. No. 6,512,005 describes a procedure for the purification of Warfarin acid. Sodium, potassium and lithium Warfarin salts and the corresponding clathrates are prepared in high, pharmacopeial grade purity and good yields from the pure Warfarin acid and the respective metal salt bases in suitable media.
WO 02/070503 describes an improved procedure for the purification of Warfarin acid. Sodium, potassium and lithium Warfarin salts and the corresponding clathrates are prepared in high, pharmacopeial grade purity and good yields from the pure Warfarin acid and the respective metal salt bases in suitable media. The process for preparing pure Warfarin acid from crude Warfarin acid starts by suspending the crude acid in a water immiscible solvent, extracting the acid into an aqueous solution of dilute base, separating the resulting aqueous phase and diluting it with a lower alkyl alcohol. The aqueous solution is filtered before being diluted with the lower alkyl alcohol. The solution is acidified to a pH of about 2 to 5 using a suitable acid, such as hydrochloric, sulfuric or phosphoric acid. The resulting suspension is stirred at a temperature of from about to 20° C. to about 60° C., cooling the suspension below room temperature, filtering the pure Warfarin acid and drying.